The present invention relates to a plasma etching method, and more particularly to a plasma etching method for plasma etching a magnetic material.
Today, development efforts are underway for a magnetoresistive random access memory (MRAM) in which data is stored in a magnetic tunnel junction (MTJ) device (hereinafter referred to as an MTJ device) by utilizing the giant magneto resistive (GMR) effect or the tunnel magneto-resistance (TMR) effect. An attempt is now made to form an MTJ device, which includes a magnetic material, by performing plasma etching.
For example, JP-A-2005-314791 discloses a method in which high frequency is used to generate plasma from reaction gas, which contains hydrocarbon compound gas, gas of a compound having oxygen atom, and gas of a compound having nitrogen atom, and the metallic magnetic material film is etched using this plasma. This document also discloses that a fluorocarbon compound is used as the etching gas.
However, the problem with this method is that a conductive magnetic film is formed on the side wall of an MTJ device with the result that the magnetic films, provided on and under the insulator, are short-circuited. Thus, the insulator used in this method does not show a great magneto-resistance effect.
To solve this problem, JP-A-2003-78184 discloses a method in which a first magnetic layer, a non-magnetic layer, and a second magnetic layer are dry-etched in this order.
At this time, though a fence is formed by a re-deposit on the work cross-section (that is, on the device side wall), this method uses nitrogen as the etching gas to increase the electric resistance of the re-deposit so that the decrease in the magnetic resistance effects of the film can be reduced.